G-proteins are best described as

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G-proteins are best described as

G-proteins act as molecular switches at the cell membrane. They are mobile membrane-associated heterotrimers made of alpha, beta, and gamma subunits that bind GDP when inactive and GTP when active. When a GPCR receives a signal, it promotes GDP release and GTP binding on the alpha subunit, causing it to change shape and often separate from the beta–gamma dimer to regulate downstream effectors. The cycling between GDP- and GTP-bound states is what allows these proteins to relay signals from receptors to intracellular targets. This description fits best because it captures their subunit composition, membrane association, and nucleotide-binding switch mechanism, unlike options that describe receptor kinases, cytosolic steroid receptors, or structural cytoskeletal components.

G-proteins act as molecular switches at the cell membrane. They are mobile membrane-associated heterotrimers made of alpha, beta, and gamma subunits that bind GDP when inactive and GTP when active. When a GPCR receives a signal, it promotes GDP release and GTP binding on the alpha subunit, causing it to change shape and often separate from the beta–gamma dimer to regulate downstream effectors. The cycling between GDP- and GTP-bound states is what allows these proteins to relay signals from receptors to intracellular targets. This description fits best because it captures their subunit composition, membrane association, and nucleotide-binding switch mechanism, unlike options that describe receptor kinases, cytosolic steroid receptors, or structural cytoskeletal components.

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